Several prior art methods of depositing and protecting dielectric-metal coatings are known such as the method described in U.S. Pat. No. 7,648,808 issued to Buchsbaum, et al., which deals with a final blanket coat deposited on top of patterned features. In the Buchsbaum disclosed method, features are patterned and deposited using a lift off process followed by a novel final blanket coating step that completes the coating stack and results in passivation of the metal layer edges. The passivation of the metal layer edges prevents oxidation and corrosion of the metal. The final blanket layer can be a group of layers such as a final cavity mirror or anti reflection layers or a single layer of a material. These layers may use materials specifically selected for their corrosion resistant properties. This prior art technique is compatible with partially or fully populated patterned areas but utilizes a continuous blanket coating over the coated and uncoated patterned regions. It is not compatible with wafers with bond pads or similar uncoated area requirements. Prior art described in Patent No. EP2746739 A2 describes methods of depositing dielectric-metal coatings by which the metal in these coatings have to be encapsulated by the dielectric. It is apparent to those skilled in the art that such encapsulation requires dual layer patterning like in U.S. Pat. No. 5,120,622 or deposition at special angles, Patent No. EP2746739 A2. U.S. Pat. Nos. 5,711,889, 6,638,668, and 7,648,808 issued to Buchsbaum disclose a method wherein the features are patterned and deposited using a lift-off process which utilizes an undercut. Another prior art method presently used in the industry is a dual layer patterning process that utilizes a non-photosensitive base layer under a photo sensitive resist layer (see FIG. 1 top). As shown in the bottom of FIG. 1, subsequent thermal processing can lessen or eliminate this undercut. On heating, the top layer of photoresist reflows and pulls back from the edge leading to a reduced lift-off profile. It is herein disclosed that adding a post-bake development step will aid in the lift-off process by re-creating the undercut. Thus, after the resist reflows, the substrate can be developed again to remove some of the non-photosensitive base layer. Since the photoresist has been exposed and baked, it will not be affected by the extra develop. This post-bake develop has also been imaged by SEM (See FIG. 2). These SEM images show that a second develop can be employed to re-create the undercut. In applications requiring encapsulation of a first deposited film by a second deposited film, the photoresist profile has to be sloped to permit the second deposited film to effectively encapsulate the first film. The invention of this disclosure provides the line of sight for the encapsulation whilst still maintaining the undercut in the liftoff profile (See FIG. 3).
By using the lithography process disclosed in this application the prior art's limitations described above can now be overcome.